1. Field of the Invention
The present invention relates to a frame structure used in a medium access control (MAC) system using a channel hopping method, and more particularly, to a new frame structure for preventing a channel hopping sequence from being depleted due to an increase in the number of nodes in a MAC system operating on a wireless ad-hoc network, and a frame structure used to constitute a star network topology necessary to efficiently operate a network.
2. Description of the Related Art
A wireless sensor network relays and transmits sensing information in a multi-hop system using low power inexpensive nodes so that the sensing information may be used to provide a monitoring service. A wireless sensor network is installed and operated in an independently isolated radio frequency (RF) environment. However, when the wireless sensor network uses heterogeneous wireless devices (e.g. wireless local area network (LAN), Bluetooth, etc.) using the same RF band, the performance of a wireless communication system deteriorates due to signal interference. Frequent retransmission causes an increase in power consumption and a delay in transmitting the sensing information.
Wireless interference signals are divided into self-interference signals and mutual interference signals. Self-interference signals are generated by wireless devices that execute the same type of applications. Mutual interference signals are generated by different types of wireless devices that use the same RF band. Self-interference signals mainly use MAC methods such as a frequency division method using signal orthogonality, a time division method, a code division method, and the like.
The IEEE 802.15.4 MAC is a representative technology for realizing a real-time high reliability service in a low power based wireless sensor network.
However, a MAC system uses a single frequency during the use of a link and thus it is weak in terms of interference signals having the same RF band and is difficult to variably schedule a communication link bandwidth. Also, when limited wireless channels are hopped in the MAC system, an available channel hopping sequence is depleted due to an increase in the number of mesh nodes.
Sensing information of the wireless sensor network is required to minimize a transfer delay time according to an available application, which needs a flexible network structure comprising a combination of a perpendicular star topology that manages nodes of a network end for obtaining the sensing information as a single node and a peer-to-peer (mesh) topology that horizontally connects information collected in a star type end group and relays the information.